This invention pertains to catalytic two-stage hydrogenation and liquefaction of coal using temperature staged ebullated-bed catalytic reactors to produce low-boiling hydrocarbon liquid products. It pertains particularly to such a process in which used catalyst is removed from a lower temperature first stage ebullated-bed reactor and cascaded forward to a higher temperature second stage ebullated-bed reactor for further use, so as to reduce the fresh catalyst requirements for the process.
In the catalytic hydrogenation and liquefaction of coal to produce hydrocarbon liquid products, various two-stage catalytic processes have been proposed including processes utilizing relatively low first stage reaction temperatures of only 600.degree.-750.degree. F. Examples of such prior coal liquefaction processes using two catalytic reaction stages connected in series are disclosed by U.S. Pat. Nos. 3,679,573, 3,700,584, 4,111,788, 4,350,582, 4,354,920, and 4,358,359. In such catalytic coal liquefaction processes, the catalyst costs are significant due to catalyst deactivation caused by carbon and metals deposition on the catalyst, which requires replacement with fresh or regenerated catalyst. Usually the catalyst in the reactors undergoes rapid deactivation due to accumulation of carbon and metals, such as calcium, iron, titanium, etc. Recognizing this problem, U.S. Pat. No. 3,679,573 to Johnson discloses a catalytic two-stage coal liquefaction process in which used catalyst is removed from the second stage reactor and further utilized at the same reaction conditions in the first stage reactor, where the catalyst accumulates deposits of metallic contaminants such as titanium in the form of titanium dioxide which rapidly deactivates the catalyst, so that it requires replacement sooner or at a higher rate than is economically desirable. Thus, the used catalyst is transferred from the second to the first stage reactor countercurrent to the coal feed direction.
But contrary to the teachings of this Johnson patent and the prior art, we have unexpectedly discovered that carbon and metals deposits on the used catalyst in a lower temperature first stage reactor does not prevent its effective use in a higher temperature second stage reactor. We have now developed a process for catalytic two-stage hydrogenation and liquefaction of coal in which used catalyst removed from the lower temperature first stage catalytic reactor has been unexpectedly found desirable and useful in the higher temperature second stage catalytic reactor, so that the total consumption of fresh catalyst per unit quantity of coal processed is significantly reduced.